This invention relates to an article with a polymeric surface having permanent indicia thereon and to a method of producing permanent indicia on a polymeric surface.
Substrates such as wires, cables, equipment housing and the like are sometimes labeled with marker assemblies comprising a polymeric article marked with indicia, such as letters or numbers or combinations thereof. To identify individual wires of a harness the marker assembly may comprise a sleeve, preferably heat recoverable, of a polymeric material such as a polyolefin, a vinylidene fluoride polymer or the like. Heat-recoverable marker sleeves are described in U.S. Pat. Nos. 3,894,731 to Evans and 4,349,404 to Changani et al. and U.S. patent application Ser. No. 07/221,708, filed Jul. 20, 1988, the disclosures of which are incorporated herein by reference. Such sleeves are provided in a variety of colors, including black, for color coding the wires. Relatively flat polymeric articles may be used for similarly marking large diameter cables and electrical equipment. The indicia are generally typed onto the article using typewriting or similar printing equipment. Generally, the ink used is black.
For many uses, the indicia need to be permanent e.g. resistant to being rubbed off and resistant to solvents which may contact the wire, as discussed more fully below. This latter requirement is generally specified for aircraft wiring, which may come into contact with hydraulic fluid, liquid fuel, de-icing solvents or the like. Indicia comprising black ink on polymeric surfaces are generally rendered permanent by a heat treatment. This heat treatment, referred to as permatization, may take place by subjecting the sleeve to infrared (IR) radiation. For some heat-recoverable sleeves, the heat applied during the heat-recovery step may be adequate to permatize the indicia. It is believed that during permatization, the black ink is preferentially heated and the carbon black of the ink undergoes a physical and/or chemical interaction with the polymeric surface rendering the indicia permanent. Obtaining a visible permanent mark on articles with other than black ink has necessitated use of a relatively expensive "hot-stamping" technique. For example, attempts to print black marker sleeves with permanent white indicia by applying white ink and then permatizing in conventional permatizers have typically been unsuccessful. The black sleeve tends to heat preferentially rather than the ink and this can lead to damage of the sleeve, particularly in its central region. It also has been noted that indicia toward the outer edges of the sleeve may be inadequately permatized. If the energy output of the IR source is increased to prevent this, the sleeve may be damaged or split.
We have now discovered that permanent, contrasting indicia can be obtained on a polymeric surface by use of an appropriate ink and an appropriate permatizing treatment, as discussed hereinafter.